Various methods and structures have been provided for recovery of waste heat from gas streams. However, in so far as is known to me, various conventional heat recovery systems have generally not optimized the recovery of heat available from the incoming gas stream. For example, traditional prior art indirect coil economizers are relatively inefficient. And, prior art condensing systems for combustion gas streams have not optimized various process elements. Thus, it would be advantageous if a heat recovery system were provided that enabled use of a much higher overall heat transfer coefficient than is presently found in prior art devices such as a standard dry coil economizer.